Journal Article

Supervised versus unsupervised approaches to classification of accelerometry data

Astell, Molly, Brandt, Joseph, Sur, Maitreyi, Katzner, Todd E., Hall, Jonathan C., Poessel, Sharon A.

2023

Overview

Sophisticated animal‐borne sensor systems are increasingly providing novel insight into how animals behave and move. Despite their widespread use in ecology, the diversity and expanding quality and quantity of data they produce have created a need for robust analytical methods for biological interpretation. Machine learning tools are often used to meet this need. However, their relative effectiveness is not well known and, in the case of unsupervised tools, given that they do not use validation data, their accuracy can be difficult to assess. We evaluated the effectiveness of supervised (n = 6), semi‐supervised (n = 1), and unsupervised (n = 2) approaches to analyzing accelerometry data collected from critically endangered California condors (Gymnogyps californianus). Unsupervised K‐means and EM (expectation–maximization) clustering approaches performed poorly, with adequate classification accuracies of <0.8 but very low values for kappa statistics (range: −0.02 to 0.06). The semi‐supervised nearest mean classifier was moderately effective at classification, with an overall classification accuracy of 0.61 but effective classification only of two of the four behavioral classes. Supervised random forest (RF) and k‐nearest neighbor (kNN) machine learning models were most effective at classification across all behavior types, with overall accuracies >0.81. Kappa statistics were also highest for RF and kNN, in most cases substantially greater than for other modeling approaches. Unsupervised modeling, which is commonly used for the classification of a priori‐defined behaviors in telemetry data, can provide useful information but likely is instead better suited to post hoc definition of generalized behavioral states. This work also shows the potential for substantial variation in classification accuracy among different machine learning approaches and among different metrics of accuracy. As such, when analyzing biotelemetry data, best practices appear to call for the evaluation of several machine learning techniques and several measures of accuracy for each dataset under consideration. Despite the widespread use of advanced bio‐logging tools, the quantity of data they produce has created a need for robust analytical methods for biological interpretation. Here we evaluate the effectiveness of 6 supervised, 1 semi‐supervised, and 2 unsupervised machine learning tools for the analysis of acceleration data from critically endangered California condors. Unsupervised classification, which is commonly used for the classification of a priori‐defined behaviors in telemetry data, likely is instead better suited to the post hoc definition of generalized behavioral states.

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc,Wiley
• Subject: accelerometer / Accelerometers / Accuracy / animal behavior / Applied Ecology / Behavior / Behavioural Ecology / Best practice / Biodiversity / California condor / Classification / Clustering / Data analysis / Data collection / Digital cameras / Effectiveness / Endangered species / Evaluation / Global positioning systems / GPS / Learning algorithms / Machine learning / Modelling / Social interaction / Statistics / Telemetry